The mice were set a range of tasks to assess whether their memories improved after receiving the hormone.

Professor Christian Holscher, who co-authored the study, said the hormone used to stimulate insulin production also protects neurons - nerve cells inside the brain which are crucial for normal brain function.

"They keep the cells healthy for much longer, the neurons are much tougher, so to speak, and they will function properly for much longer," he said.

"This is a very exciting time for us. It does look very promising but we have to wait for the clinical trial now to see the effects on humans."

A clinical trial on humans is due to begin this year.

Prof Holscher explained how the tests on the rodents were carried out: "We presented the mice with different objects.

"They are naturally very curious and explore and sniff these new objects but once they have done this they are no longer interested in them. We tested to see whether they remembered if they had seen the objects before. They were also put in small swimming pools with a platform to get out and we watched to see whether they remembered the location of the platform.

"They were also tested to see if they could remember where food was located. There were a variety of learning tasks and the mice who received the hormone showed a small improvement in some of the learning and memory tasks."

The planned clinical trial will be open to people showing early symptoms of Alzheimer's disease. It will aim to ascertain exactly how the drug affects the brains of people with Alzheimer's disease but Prof Holscher said he is optimistic the results will be positive.

He continued: "This would be a huge breakthrough because at the moment there is really no treatment for people with Alzheimer's.

"There has been a huge amount of research done over the years and none of the other drugs have ever done anything in terms of treating patients so it has been extremely frustrating for researchers."